Lower Helderbero Brtozoa and Corals. 103 



the border a somewhat lobed appearance ; cells arranged irregularly 

 and at distances varying from one-half to nearly twice their own 

 length. Intercellular spaces marked by minute shallow pits, which 

 are easily worn away, giving to the branches the appearance of 

 Trematopora. In well preserved individual branches the intercellu- 

 lar pits are distinct, and the borders of the cells have small, short 

 spines. 



This is a common and variable species, occurring in branches of 

 from three-hundredths of an inch to a line or more in diameter ; the 

 pores also vary in size and contiguity. 



Formation and locality. — In the shaly limestone of the Lower 

 Helderberg group, near Clarksville, Albany county, New York. 



Callopora ponderosa n. sp. 

 Bryozoum growing in heavy, dense, irregular masses, formed by 

 numerous accretions of growth; or in smaller masses, incrusting 

 shells and other substances. Surface crowded with medium-sized 

 circular cells, distant from each other about half their own diameter, 

 margins not elevated above the surrounding surface. Intercellular 

 spaces crowded with minute, deep, polygonal pits, in one, two, or 

 sometimes three ranges ; the small triangular spaces at the angles, 

 between the cells and pits, are elevated and form short triangular 

 spines. 



This species somewhat resembles in surface characters the C. ele- 

 gans of the Niagara limestone, but it is of finer texture, and the cells 

 have not the tendency to form rows, so common in that species. It 

 differs from C. jperelegans in the smaller size of the pores, the more 

 numerous and smaller intercellular pits, and in its mode of growth, 

 which is always incrusting or in large irregular masses. 



Formation and locality. — In the shaly limestones of the Lower 

 Helderberg group, at Schoharie, New York. 



Genus TREMATOPORA Hall. 



Trematopora rbombifera n. sp. 

 Bryozoum forming slender solid branches, with distant diverging 

 ramifications ; their surface marked by densely crowded, rhombic 

 pores with narrow partition walls, carinate on their edges. Cells 

 generally equal-sided, and arranged spirally around the branch, their 

 vertical greater than their transverse diameter. The branches vary 



